1. Field of the Invention
The present invention relates to improvement of a gasket holding device used for holding a metallic gasket aiming at preventing leakage of fluid in a ultra-high vacuum apparatus for use in an semiconductor manufacturing apparatus, a nuclear apparatus and the like and for disposing the same metallic gasket at a predetermined position between flanges.
2. Description of Related Art
Conventionally, various kinds of the metallic gaskets are used in the semiconductor manufacturing apparatus and the like in order to obtain a high vacuum condition.
The aforementioned gasket is applied fittingly so as to clog a gap between two components adjacent each other such as flanges, so that it is disposed in a groove or the like between the components to joint the two components.
At this time, foreign matter may adhere to a gasket or the gasket may be provided with a minute flaw upon handling, thereby leading to leakage. Further, when the gasket is installed, its position may be deflected, so that tightening of the gasket becomes unequal, thereby sometimes generating a leakage.
The reason for use of the gasket is to enable the gasket to be attached or detached to/from an apparatus without touching directly the gasket.
The generally known gasket holding device is composed of a metal thin plate which is elastically deformable and has a gasket introduction hole and a gasket supporting hole which is connected to this introduction hole. Further, if a single gasket holding device is provided with plural gasket holding portions, there is an advantage that the plural gaskets can be attached or detached all at once.
In a gas supplying unit for use in the semiconductor manufacturing apparatus, various components such as a valve, filter, regulator and mass flow controller are installed on arranged metallic blocks called substrate having a flow path. Because these components are concentrated in a narrow space, taking labor and time for replacement of any component is a problem to be solved.
In the aforementioned gas supplying unit, the gasket is inserted in between the substrate and each of various components and fit to the groove in the substrate. To facilitate mounting of the gasket, often the gasket holding device having the gasket is fixed to each of various components with bolts and then, this assembly is fixed onto the substrate with bolts.
In order to hold the gasket holding device with the bolts, its bolt mounting hole is formed so as to be smaller than the outside diameter of a crest portion and larger than the outside diameter of a root portion. If such a bolt mounting hole is formed, an inner peripheral edge of the bolt mounting hole is elastically deformed and projected in between the crest and the root which constitute a bolt thread. Consequently, the gasket holding device is blocked from sliding freely on the bolt, and thereby the mounting performance of the gasket on various kinds of components is improved.
As the shape of the bolt mounting hole in the aforementioned gasket holding device, for example, circular shape, cubic shape and rectangular shape can be mentioned. When the outside diameter of the crest portion of the bolt is too small with respect to the diameter of the bolt mounting hole, the gasket holding device is likely to slip out of the bolt. When a gap between the bolt mounting hole and the outside diameter of the crest of the thread is large, a high friction occurs when the bolt is moved, so that the bolt is hard to fit.
Further, most metallic annular gaskets are as small as about 10 mm in outside diameter so as to meet miniaturization of components of a semiconductor manufacturing apparatus, so that when a gasket is mounted in a concave portion formed in a flange joint face, the gasket is likely to be deflected from its proper position. Consequently, tightening of the gasket becomes unequal, and thereby leakage may occur, foreign matter may adhere to the gasket when it is mounted or a minute flaw may be made in the gasket.
For the reason, the gasket holding device has been utilized to attach/detach the gasket to/from an apparatus without touching directly the gasket.
The gasket holding device is composed of mainly an elastically deformable thin metal plate (0.1 mm thick) and contains a gasket introduction hole and a supporting hole communicating with the hole, formed in the metal plate. The gasket is slid from the introduction hole into the supporting hole, so that it is held by the supporting hole.
A gasket holding device capable of supporting plural gaskets (3 max.) has been also known.
When the gasket holding device is employed for a gas supplying unit of a semiconductor manufacturing apparatus, particularly following matters are considered.
(1) The gas supplying unit contains a large number of components assembled in a small space.
(2) Each component has a square flat face for mounting a gasket holding device and the respective components are arranged in line.
(3) Each component has a groove for receiving the gasket.
(4) The number of gaskets used for a single component differs depending on the component.
(5) If a groove for receiving the gasket is provided, the groove is disposed in the center of a component. If plural grooves are provided, the grooves are disposed in the center and near the center of the component.
When a gasket is attached to or detached from the above-described gas supplying unit, there are following problems.
In the case where mounting of a gasket on an apparatus is forgotten, it is possible to verify whether or not the gasket has been mounted through a fluid leak test. However, because a large number of components are provided in the apparatus, it is difficult to confirm which component misses the gasket or whether or not a necessary number of the gaskets are loaded even if some gaskets are provided.